Many types of pressure control valves are already known within the state of the technology. Many of these said valves were used as servo valves in the regulation of clutches in automatic motor vehicle transmissions. In such transmissions, the hydraulic pressure is found to be about 10 bar or greater. This initial pump pressure is normally reduced by a pressure reducing valve to a service pressure of about 5 bar, to which is subjected a pressure control valve. The pressure control valve of concern, for example, is designed as a proportional control valve. After a clutch has been engaged, in order to hold said clutch in that selected stage, normally a safety-factor excess pressure, which generally represents the system pressure, is applied to the clutch cylinder and by means of additional, pressure retaining valves, the said pressure is maintained. With this arrangement, three valves, namely a proportional pressure control valve, a pressure reducing valve, and a pressure-retaining valve, are required for the operation of a clutch in an automatic transmission.
Other pressure control valves have been proposed, which fulfill all of the above functions, and thereby offer simplified construction. A proportional pressure regulating valve, which serves as a pilot valve is provided with a pressure reducing and a pressure-holding function, is described in DE-A 199 04 901. In the case of this known pressure control valve, a proportional solenoid is provided, which, in its scope of operation, approaches a constant strength of magnetism. This proposed pressure control valve possesses a valve housing, a control element for opening and closing a throttle port and has an armature rod for the connection of the control element, the rod being actuated by a proportioning solenoid. The valve further has a solenoid core, a solenoid armature and a solenoid coil, to the end that the solenoid armature rod is axially displaceable, moving back and forth between two defined end positions.
For the control of the pressure in hydraulic circuits, with assist from pressure control valves of the described kind, the basis is, that by means of the proportional solenoid, the coil current is regulated to be proportional to the size of the output force. That is, the solenoid armature and thereby a valve throttling element related to said armature, controls the demands of a clutch, in accord with the coil current. Thus, a desired pressure-current-characteristic curve for an electro-hydraulic control of automatic transmission is thus produced from the solenoid-current-characterization curve of the pressure control valve.
DE-A 100 34 959 of the applicant, discloses a proportional pressure control valve having a valve component with in and out ports and with at least one means for the proportional control of an aperture, as well as having a solenoid component, which possesses a solenoid core, a solenoid coil and a slidingly displaceable solenoid armature. To accomplish the desired purpose thereof, an activation element acts in concert with the solenoid armature, which activation element initiates a spherical shutoff means. In accord therewith, the hydraulically responsive cross-section of the aperture is essentially determined by the length of the aperture assembly, the diameter thereof, and the diameter of that part of the activation element which impinges therein.
Proposed in a non-published application of the applicant under file number DE 102 55 414.5 is a proportional pressure control valve for the regulation of pressure in a hydraulic circuit, especially in a hydraulic circuit for a vehicle transmission, wherein the pressure-current characteristic curve exhibits, at least partially, a very flatly rising curve at low current, and conversely at greater current, a very sharp pressure-current slope. This pressure control valve possesses a push rod as a connection between a control element in the hydraulic circuit and a proportional magnet in the housing, which has a solenoid core, a solenoid armature, and a coil. Further in this case, the solenoid coil and the solenoid core are securely bound to the housing. In the interior space of the solenoid coil, the armature, is axially moveable back and forth between end positions by a magnetic force existing between within the air space between the solenoid armature and the solenoid core (solenoid core=the magnetic control edges) for the purpose of activating the control element. At least a part of the solenoid armature is moveably placed in relation armature rod, as determined by the magnetic flux, so that, in this manner, either the air space is enlarged by said movability, and/or an additional, second air space is created.
Since the hydraulic pump of a transmission, usually produces strong pulsations, which are transferred to all moveable parts in the said transmission, it is possible that vibrations can be imparted to the armature of electromagnetic pressure control valves, which vibration in turn, can be transmitted to the clutches. For this reason, very frequently, electromagnetic pressure control valves are provided with damping chambers, which soften the axial movements of the armature. The armature is enclosed by a magnetic coil and a magnetic core for the purpose of bringing about the mentioned axial movements. In order, that such pulsation related vibrations can be avoided, in DE-A 196 06 381, a pressure regulator for electro-hydraulic transmission control was proposed, which was designed as a valve seat operated control with a solenoid coil and a core, which encased an armature, which is axially, slidably displaceable by the magnetic force in its given space. The armature is carried both in a forward and a rearward set of bearings. Further, the pressure regulator possesses a push rod, which on its one end connects with an end face of the armature rod in the area of its forward bearing, or it is loosely carried thereon adjacent to the armature and on its other end, is secured in a gate assembly for an oil through-flow boring and is aligned therein by a push rod guide. The armature space is divided by the armature into two damping chambers. Between an adjustment apparatus and the rear bearing of the armature, is formed a oil filled damping chamber on the end remote from the push rod. The closure housing possesses a greater diameter than does the push rod and between the forward bearing of the armature and the push rod, is a damping chamber filled with oil, which is connected with the armature space by means of a relief boring.
In another unpublished application of the applicant, under the file number of DE 102 48 181.4, an electrical pressure controller valve has been proposed, which, reacts quickly to current changes and if disturbed by an overload, handles the said disturbance without changing any preset operational values. In order to support damping, not only by means of the outside diameter of the armature and its bearings, in this proposed pressure control valve, an armature rod is centrally bored by a axial, longitudinal opening, into which a pin is inserted with preselected clearance. Thereby, the active length of the surface, frictionally reacting to oil viscosity, can be differently shaped, and be expanded several times. The said inserted pin is fastened onto the throttling passage assembly, which is present in the case all known pressure control valves, and is actually in the form of threaded adjustment body. By means of a simple extension of this adjustment body, a counter surface in the boring can be created.
By means of the insertion of this pin, the dimensions of which are complementary to dimensions of the said longitudinal boring, the said pin fits into the longitudinal boring with little play, whereby additional damping is created because of oil viscosity, which damping can be increased by additional, transverse borings in the pin, which lead to a discontinuous event in the characteristic curve.
Besides these disturbing influences caused by pulsation, temperature swings also act disadvantageously against operation of the electrohydraulic pressure controller. This is because this pressure controller exhibits strong regulatory drifts during temperature changes. That is to say, the operating pressure for the control of the valve gate, which, with constant flow, regulates in a defined manner, will change in accord with temperature variation.
In order to exclude this disadvantageous influence, efforts have been made, to use expensive and costly materials, notably plastics, for the moveable valve flow positioning members, in order to bring the damaging temperature drift into a manageable range. However, the difficulty lies not in the expense of the material, but rather in the cost of fabricating the material. Further trials to solve the problem were made by complex software controls, which depend on the installation of a temperature sensor. Such software controls endeavor to hold to a minimum the pressure differences at the valve gate, caused by the pressure controller by means of corresponding feedback control. This goal can only be achieved to a limited extent.
The purpose of the invention is to create a simple, reliable and economical apparatus, in order to substantially reduce the temperature drift of the presently used electro-hydraulic pressure control valves.